The present invention relates to liquid-liquid contacting columns for solvent extraction, stripping, scrubbing, washing, re-extraction and similar operations, and in particular it concerns a liquid-liquid contacting column for effecting multiple operations using a novel intermediate decanter.
It is known that the purpose of liquid-liquid contacting columns for solvent extraction is to recover solute dissolved in one liquid phase, usually an aqueous phase, by extracting the solute with a suitable solvent, usually an organic phase as the other liquid phase, and which becomes the extract. Optionally and typically, the extract is subsequently purified or scrubbed by a suitable scrubbing agent (usually another aqueous phase) to remove undesired contaminants. This unit operation is often followed by a stripping or re-extraction stage in which a suitable stripping agent (usually another aqueous phase) is used to recover the purified product.
In defining a stage as the combined operation of contacting the two participating liquids, allowing them to reach equilibrium by mixing and mechanically separating them by settling, it follows that solvent extraction is, basically, a multi-stage process. Any mixer and settler can be combined to produce one solvent extraction stage, and stages can be arranged in a multi-stage battery.
Many arrangements have been invented in an effort to reduce inter-stage operational volumes, pumping and costs. Some examples are the xe2x80x9cBoxxe2x80x9d-type described by Coplan et al., Chem. Eng. Prog. 50, 403 (1954), or a further modification described by Hazen et al., Min. Eng. 994 (1957), among others.
Other approaches to solvent extraction have been suggested, such as U.S. Pat. No. 3,017,253 to Coleby, which teaches a Graesser extractor that is based on an horizontal shell with a series of buckets revolving around an inner shaft dropping droplets of one liquid through the other.
A more advanced equipment category for solvent extraction allows continuous and differential operation. The equipment in this category is usually arranged for multi-stage, countercurrent contact of the two participating liquids, without complete repeated separation of the liquids between adjacent stages. Instead the liquids remain in continuous contact while flowing through the equipment. Typical examples of this category are the various types of extraction columns.
Countercurrent flow is maintained in the equipment by the difference in densities of the liquids and the force of gravity. Both liquids are pumped through the equipment at any desired linear velocity and selected phase ratio.
In many cases, the density difference between the liquids is insufficient to disperse one liquid in the other and to keep turbulence at the requisite level for efficient mass transfer. Various mechanical stirring or pulsation devices may apply additional energy needed for reaching the desired turbulence. U.S. Pat. No. 2,601,674 to Reman et al., for instance, relates to a rotary disk contactor, which is an example of a mechanical stirred continuous device, while U.S. Pat. No. 2,011,186 to Van Dijk is an example of a pulsed column.
In pulsed columns, a reciprocating motion is applied to the main column cylindrical section to agitate the liquids, provide the desired turbulence and thus improve the rate of mass transfer. Reciprocating plungers or pistons can be used as pulsing devices. A more current approach uses air pulsing devices. Beneath and beyond the extraction column cylindrical section, in which the mass transfer takes place, there are usually placed settling decanters, each of a suitable volume, for proper separation of each of the two liquid phases. The clear light phase flows out the top of the column and the clear heavy phase flows out the bottom.
As described briefly above, solvent extraction is often followed by purifying or scrubbing the extracted phase from undesired contaminants, and by recovering the purified product by stripping. Performing these tasks necessitates at least one, usually more, additional columns, and additional equipment such as settling decanters, holding tanks, pumps, control devices, pulsing means, etc.
Theoretically, appreciable savings in equipment and energy (as well as improvements in process ecology in many applications) could be achieved by building a single column in which multiple process stages are integrated. However, although feeding an extraction column via an intermediately disposed feed port is relatively straightforward, the selective removal of a given phase via an intermediately disposed discharge port is, to the best of our knowledge, unknown in the art, and has certainly not seen widespread commercial implementation. Moreover, to date, there is no known prior art system for and method of, performing several countercurrent operations in series in a single column.
There is therefore a recognized need for, and it would be highly advantageous to have, a system for, and a method of, solvent extraction that has the ability to extract and purify and recover materials in a single, integrated column.
The present invention is a system for, and a method of, liquid-liquid contacting for performing solvent extraction and stripping, scrubbing and similar additional operations, in a single, integrated column.
According to the teachings of the present invention there is provided an intermediate decanter in a liquid-liquid contacting system. The decanter, disposed between an upper contacting column and a lower contacting column, includes: (a) a housing having: (i) a top opening communicating with the upper column; (ii) a bottom opening communicating with the lower column; and (iii) a decanter outlet designed and configured for discharging a substantially heavy phase. The intermediate decanter further includes: (b) a first partition within the housing forming a first settling chamber and a second settling chamber. The first partition is designed and configured within the housing so as to direct a flow of a substantially light phase received from the lower column through the second settling chamber, wherein the light phase is separated from the heavy phase of the lower column, into the first settling chamber, wherein the light phase is separated from the heavy phase of the upper column. The heavy phase is in communication with the decanter outlet, for discharge thereto, and the light phase is in communication with the upper column, for discharge thereto.
According to another aspect of the present invention there is provided an integrated column for performing a plurality of liquid-liquid contacting functions. The column includes: (a) an upper column section; (b) a lower column section, and (c) an intermediate decanter fluidly connecting between the upper column section and the lower column section. The intermediate decanter includes: (i) a housing having: (A) a top opening communicating with the upper column section; (B) a bottom opening communicating with the lower column section, and (C) a decanter outlet designed and configured for discharging a substantially heavy phase therefrom. The intermediate decanter further includes: (ii) an inner workings including: a first partition designed and configured within the housing so as to form a first settling chamber and a second settling chamber, and so as to direct a flow of a substantially light phase received from the lower column section through the second settling chamber, wherein the light phase is separated from the heavy phase of the lower column section, and into the first settling chamber. In the first settling chamber the light phase is separated from the heavy phase of the upper column section and discharged through to the upper column section, while the heavy phase is discharged though the decanter outlet.
According to yet another aspect of the present invention there is provided an integrated column for performing a plurality of liquid-liquid contacting functions. The column includes a plurality of units, each including: (a) a column section, and (b) an intermediate decanter fluidly connected to a first end of the column section. These units are attached in series, such that each intermediate decanter in the integrated column is connected to an upper column section and a lower column section. Each intermediate decanter includes: (i) a housing having: (A) a top opening communicating with the upper column section; (B) a bottom opening communicating with the lower column section, and (C) a decanter outlet designed and configured for discharging a substantially heavy phase therefrom. Each intermediate decanter further includes: (ii) an inner workings having: a first partition designed and configured within the housing so as to form a first settling chamber and a second settling chamber. The first partition designed and configured to direct a flow of a substantially light phase received from the lower column section through the second settling chamber, wherein the light phase is separated from the heavy phase of the lower column section, and into the first settling chamber. In the first settling chamber the light phase is separated from the heavy phase of the upper column section and discharged through to the upper column section, while the heavy phase is discharged though the decanter outlet.
According to still another aspect of the present invention there is provided a method for performing a plurality of liquid-liquid contacting operations in an integrated column. The method includes the steps of: (a) providing an integrated column including: (i) an upper column section; (ii) a lower column section, and (iii) an intermediate decanter fluidly connecting between the upper column section and the lower column section. The intermediate decanter including: (A) a housing having: (I) a top opening communicating with the upper column section; (II) a bottom opening communicating with the lower column section, and (III) a heavy phase outlet, and (B) a first partition disposed within the housing forming a first settling chamber and a second settling chamber; (b) flowing a light phase through the lower column section and through the upper column section via the second settling chamber and the first settling chamber; (c) performing a first liquid-liquid contacting operation in the upper column section by passing a first heavy phase through the upper column section to the first settling chamber, and (d) selectively removing the first heavy phase from the heavy-phase outlet.
According to one feature of the present invention, the first partition of the intermediate decanter is further disposed within the housing such that the light phase is separated in the second settling chamber from a second heavy phase, which is fed to said lower column.
According to another feature of the present invention, the first partition is attached to the housing so as to fluidly separate the intermediate decanter between a bottom region of the first settling chamber and a second bottom region of the second settling chamber.
According to further features in the described preferred embodiments, the first partition is attached to the housing so as to fully separate between the light phase in the second settling chamber and the heavy phase disposed in the first settling chamber and in fluid communication with the decanter outlet.
According to still further features in the described preferred embodiments, the first settling chamber has a liquid-liquid interface, below which is disposed the substantially heavy phase, and the intermediate decanter further including means for controlling a level of the interface.
According to yet further features in the described preferred embodiments, the means for controlling is designed to maintain the level below a pre-determined height of the first partition.
According to yet further features of the invention, the first partition is attached to the housing so as to fully separate between the light phase in the second settling chamber and the heavy phase disposed below the interface.
According to yet further features of the invention in the described preferred embodiments, at least a portion of the first partition is sloped.
According to still further features in the described preferred embodiments, the intermediate decanter also has a second partition disposed in a spaced relationship to the top section of the first partition. The second partition forms thereby a channel for passage of the substantially light phase from the second settling chamber into the first settling chamber.
According to still a further feature of the present invention, the means for controlling is designed to maintain the level at a pre-determined height below the second partition.
According to still a further feature of the present invention, the second partition is designed and configured to be length-adjustable.
According to still a further feature of the present invention, the second partition is designed and positioned to inhibit the substantially heavy phase of the upper column section from passing between the second partition and the housing and into the second settling chamber.
According to yet a further feature of the present invention in the described preferred embodiments, the intermediate decanter further includes at least one opening for attaching a level control instrument.
According to yet a further feature of the present invention in the described preferred embodiments, the intermediate decanter further includes at least one additional opening for attaching indicating instruments and control instruments.
According to yet a further feature of the present invention, the intermediate further includes at least one additional opening, disposed in the housing near a top of the second settling chamber, for releasing of air trapped below the second partition.
According to still further features of the present invention, the intermediate decanter further includes at least one additional opening disposed in the housing near the bottom of the first settling chamber, for draining any liquid in the first settling chamber.
According to still further features of the present invention, the integrated column further includes means for flowing the substantially light phase from the lower column section, through the intermediate decanter, and into the upper column section.
According to still further features of the present invention in the described preferred embodiments, the integrated column further includes a pulsation system including at least one pulsation generator, each connected to the integrated column, the pulsation system for promoting liquid-liquid contacting.
According to still further features of the present invention, the method further includes the step of performing a second liquid-liquid contacting operation in the lower column section by flowing a second heavy phase through the lower column section.
According to yet further features of the present invention, substantially all of the second heavy phase flowing into the second settling chamber by entrainment is settled in the second settling chamber.
According to yet further features of the present invention, the method further includes the step of controlling a liquid-liquid interface within the first settling chamber.
According to still further features of the present invention in the described preferred embodiments, the method further includes the step of providing a second partition disposed in a spaced relationship to the top section of the first partition, the second partition forming thereby a channel for passage of the substantially light phase from the second settling chamber into the first settling chamber.
According to still further features of the present invention in the described preferred embodiments, the method further includes the step of disposing the first partition within the housing so as to fluidly separate between a first bottom region of the first settling chamber and a second bottom region of the second settling chamber.
According to still further features of the present invention, the flowing of the first heavy phase through the upper column section is achieved by gravitation.
According to still further features in the described preferred embodiments, the first liquid-liquid contacting operation is selected from the group consisting of extraction, scrubbing, stripping, washing, re-extraction and reacting.
According to still further features of the present invention in the described preferred embodiments, the second liquid-liquid contacting operation is selected from the group consisting of solvent extraction, scrubbing, stripping, washing, re-extraction and reacting.
According to a further feature of the present invention in the described preferred embodiments, the first liquid-liquid contacting operation and the second liquid-liquid contacting operation are different contacting operations.
The present invention successfully addresses the shortcomings of the existing technologies by providing a system for, and method of, liquid-liquid contacting for performing various liquid-liquid contacting operations such as solvent extraction, stripping, scrubbing, washing, re-extraction and reacting in a single, integrated column. The ability of the integrated column, which is based on the intermediate decanter of the present invention, to perform the entire operation of solvent extraction plant in a single column has many technical and economical advantages. Investment costs significantly decrease due to the decrease in the number of columns, decanters, and auxiliary equipment: tanks, pumps, piping, pulsation systems, control instruments etc., and therefore, spare parts and materials inventories are also reduced relative to a standard prior art plant. At the same time, the requisite area for the plant is substantially reduced. Operating and maintenance costs also decrease due to less pumping between columns and less equipment in operation. In addition, operational safety and ecology are improved due to less solvent volumes required for the integrated column as compared to two, or more separate columns of same functionality, and simpler operation and control.